Genetic Variation In Survival Research Articles

Evidence of early genetic variation in survival and growth traits of baobab (Adansonia digitata L.)—the way forward for domestication and breeding

Evidence of early genetic variation in survival and growth traits of baobab (Adansonia digitata L.)—the way forward for domestication and breeding

Within-family variation in larval viability and growth is controlled by different genes: a case study with Crassostrea gigas

Variation in growth and survival of planktonic larvae has profound effects on marine population abundance. Environmental causes of differential larval growth and mortality are well studied, but genetic variation in these traits is less well understood. Here, we reveal genetic variation in survival and growth of full-sib larvae of the Pacific oyster Crassostrea gigas reared under identical conditions. We size-selected 1.42 million, 24 d old larvae to produce small, medium, and large size classes, constituting 93% of the population. Parental tissues and a total of 144 larvae sampled from each size class were individually genotyped with a panel of 45 mapped DNA markers. Consistent with previous work, 11 markers had genotypic frequencies that differed significantly from their Mendelian expectations and, upon mapping, are explained by 6 viability quantitative trait loci (vQTL). Notably, shell-length variance among size classes maps to 6 major growth QTL (gQTL), with just 2 collectively explaining 18% of the variance. We found little overlap between vQTL and gQTL, suggesting that variation in these larval traits is controlled by different genes. This study demonstrates the feasibility of genotyping single larvae for the identification of multiple QTL. Understanding genetic variation in larval biology is important for a comprehensive understanding of marine recruitment.

Genetic variation of macronutrient tolerance in Drosophila melanogaster

Carbohydrates, proteins and lipids are essential nutrients to all animals; however, closely related species, populations, and individuals can display dramatic variation in diet. Here we explore the variation in macronutrient tolerance in Drosophila melanogaster using the Drosophila genetic reference panel, a collection of ~200 strains derived from a single natural population. Our study demonstrates that D. melanogaster, often considered a “dietary generalist”, displays marked genetic variation in survival on different diets, notably on high-sugar diet. Our genetic analysis and functional validation identify several regulators of macronutrient tolerance, including CG10960/GLUT8, Pkn and Eip75B. We also demonstrate a role for the JNK pathway in sugar tolerance and de novo lipogenesis. Finally, we report a role for tailless, a conserved orphan nuclear hormone receptor, in regulating sugar metabolism via insulin-like peptide secretion and sugar-responsive CCHamide-2 expression. Our study provides support for the use of nutrigenomics in the development of personalized nutrition.

How does parental environment influence the potential for adaptation to global change?

Parental environments are regularly shown to alter the mean fitness of offspring, but their impacts on the genetic variation for fitness, which predicts adaptive capacity and is also measured on offspring, are unclear. Consequently, how parental environments mediate adaptation to environmental stressors, like those accompanying global change, is largely unknown. Here, using an ecologically important marine tubeworm in a quantitative-genetic breeding design, we tested how parental exposure to projected ocean warming alters the mean survival, and genetic variation for survival, of offspring during their most vulnerable life stage under current and projected temperatures. Offspring survival was higher when parent and offspring temperatures matched. Across offspring temperatures, parental exposure to warming altered the distribution of additive genetic variance for survival, making it covary across current and projected temperatures in a way that may aid adaptation to future warming. Parental exposure to warming also amplified nonadditive genetic variance for survival, suggesting that compatibilities between parental genomes may grow increasingly important under future warming. Our study shows that parental environments potentially have broader-ranging effects on adaptive capacity than currently appreciated, not only mitigating the negative impacts of global change but also reshaping the raw fuel for evolutionary responses to it.

Genetic variation in survival of tilapia (Oreochromis niloticus, Linnaeus, 1758) fry during the early phase of rearing in brackish water environment (5–10ppt)

Tilapia fry viability is one of the important traits because it affects number of seed produced and marketed and, therefore, yield and economic return for hatcheries and the aquaculture industry. In the present study, we examined the effect of female body weight prior to spawning and fry birth weight on survival rates at 20 days of nursing (D20) and at 62 days (D62) (when tagged). Genetic parameters for D20 and D62 were estimated from 86,609 individual fry which were offspring of 63 sires and 77 dams in the sixth generation of a Nile tilapia (Oreochromis niloticus) population undergoing selection for high growth in brackish water environment. Both linear and threshold models were used to estimate genetic parameters for these two traits. The estimates of heritability for D20 after hatching were low and not significantly different from zero across the models studied. By contrast, D62 showed a large heritable additive genetic component on both the liability and observed scales (h2 = 0.24–0.79). The maternal and common environmental effects were 6–12% for survival at 20 days (D20), whereas they were small for survival from 21 days to tagging, D62 (1–5%). Genetic correlation between D20 and D62 was high and positive (0.72 ± 0.06). However, the estimate was significantly different from one, which suggests that D20 and D62 are under different genetic control and should be treated as different traits in selective breeding programs for tilapia. The results from the present study indicate for the first time that there is potential for simultaneous improvement of both survival rates at 20 days of nursing and at tagging in the future genetic improvement program for this tilapia population.

Identification and utilization of donor and recipient genetic variants to predict survival after HCT: are we ready for primetime?

Overall survival following hematopoietic cell transplantation (HCT) has improved over the past two decades through better patient selection and advances in HLA typing, supportive care, and infection prophylaxis. Nonetheless, mortality rates are still unsatisfactory and transplant-related mortality remains a major cause of death after unrelated allogeneic HCT. Since there are no known pre-HCT, non-HLA biologic predictors of survival following transplant, for over a decade, scientists have been investigating the role of non-HLA germline genetic variation in survival and treatment-related mortality after HCT. Variation in single nucleotide polymorphisms (SNPs) has the potential to impact chemotherapy, radiation, and immune responses, leading to different post-HCT survival outcomes. In this paper, we address the current knowledge of the contribution of genetic variation to survival following HCT and discuss study design and methodology for investigating HCT survival on a genomic scale.

Trifolium interspecific hybridisation: widening the white clover gene pool

White clover (Trifolium repens) is adapted to moist, fertile soils in temperate zones. Despite its heterozygous allotetraploid nature, it lacks useful genetic variation for survival and growth in semi-arid, infertile soils. Although white clover is apparently genetically isolated in nature, 11 other taxa have so far been found that can be artificially hybridised into the wider gene pool. These species range from annuals to long-lived, hardy perennials with adaptations to stress environments, and they potentially provide new traits for the breeding of more resilient varieties of white clover. The delineation of the secondary, tertiary and quaternary gene pools is described, along with a review of interspecific hybrids achieved to date. The results of large breeding programs to integrate traits from T. nigrescens and 4x T. ambiguum are reviewed, and schemes introduced for the use of T. uniflorum, T. occidentale, T. pallescens, 2x T. ambiguum and 6x T. ambiguum. Interspecific hybrid breeding of white clover has the potential to enable the development of resilient perennial clovers for seasonally dry, infertile grassland environments in many parts of the world.

Detection of QTL in Rainbow Trout Affecting Survival When Challenged with Flavobacterium psychrophilum

Bacterial cold water disease (BCWD) causes significant economic loss in salmonid aquaculture. We previously detected genetic variation in survival following challenge with Flavobacterium psychrophilum (Fp), the causative agent of BCWD in rainbow trout (Oncorhynchus mykiss). A family-based selection program to improve resistance was initiated in 2005 at the USDA National Center for Cool and Cold Water Aquaculture. Select crosses were made in 2007 and 2009 to evaluate family-based disease survival using Fp injection challenges. From each putative F₂/BC₁ family generated in 2009, 200-260 fish were challenged in 4-7 replicates per family. Whole genome QTL scans of three F₂/BC₁ families were conducted with about 270 informative microsatellite loci per family spaced at an average interval size of 6 cM throughout the rainbow trout genome. Markers on chromosomes containing QTL were further evaluated in three additional F₂/BC₁ families. The additional F₂/BC₁ families were sire or dam half-sibs (HS) of the initially genome scanned families. Overall, we identified nine major QTL on seven chromosomes that were significant or highly significant with moderate to large effects of at least 13 % of the total phenotypic variance. The largest effect QTL for BCWD resistance explaining up to 40 % of the phenotypic variance was detected on chromosome OMY8 in family 2009070 and in the combined dam HS family 2009069-070. The nine major QTL identified in this study are candidates for fine mapping to identify new markers that are tightly linked to disease resistance loci for using in marker assisted selection strategies.

QTL for survival to UV-C radiation in Drosophila melanogaster

Purpose: The aim of this study was to investigate tolerance to UV-C (ultraviolet C, 280–100 nm) radiation in Drosophila melanogaster, implementing a quantitative trait locus (QTL) mapping approach. This is of interest to test for genetic variation in survival to UV (ultraviolet) radiation.Materials and methods: We performed a QTL scan in D. melanogaster recombinant inbred lines (RIL) constructed from parental stocks derived from a crossing between northern and southern hemisphere populations that segregated substantial genetic variation in thermal resistance in a previous study. Here, two experimental treatments were implemented: Continuous and cyclic UV-C radiation.Results: Significant QTL were detected on all three major chromosomes. Among these, multiple trait composite interval mapping revealed a significant QTL in the pericentromeric region of chromosome 2, a genome region consistently implicated in thermotolerance in previous studies.Conclusions: This study shows substantial genetic variation for UV-C radiation resistance in D. melanogaster, with QTL for survival to UV-C radiation generally overlapping with major thermotolerance QTL. The genetic architecture of UV-C radiation resistance appears to be more complex in continuously irradiated individuals.

Genetic control in the survival, growth and form of Acacia melanoxylon

Blackwood (Acacia melanoxylon R.Br.) is a high-quality appearance-grade timber species native to eastern Australia. Wide variation in its survival, growth and form, together with issues related to site selection and intensive silvicultural management, limit progress in its domestication and commercial development. To determine the effect of genetics on these traits, five blackwood progeny trials in northern Tasmania, Australia, aged between 15 and 19 years were assessed. All trials contained a variety of open-pollinated, single-tree, family collections from Tasmania, with one trial containing a selection of provenances from mainland Australia. Significant genetic variation in survival, growth and form were found. This variation was partly explained by broad scale adaptive differences across the wide geographic distribution of blackwood. Blackwood from the tropical northern range of the species had poor survival in cool temperate Tasmania. Significant differences in survival between Tasmanian seedlots were also observed. Among the Tasmanian seedlots, those from low altitudes grew better than those from high altitudes, while those from the north-east of Tasmania had significantly better growth rates than seedlots from the south-east. Seedlots from the north-west seed zone had intermediate growth rates. Significant genetic differences in the proportion of trees with single stems, and the number of large branches in the lower stem were found between Tasmanian seedlots. Early-age seedlot height was significantly positively correlated with mid-age diameter. Stem form was improved under nurse crops, but even open-grown blackwood had low percentages of trees of excellent form. These results indicate that at the broad scale, climatic matching of seed source with planting site is clearly important, however, within Tasmania there was no evidence that seedlots collected from the same region as the trials outperformed those from other regions.

Genetic parameters for resistance to Infectious Pancreatic Necrosis in pedigreed Atlantic salmon ( Salmo salar) post-smolts using a Reduced Animal Model

Infectious Pancreatic Necrosis Virus (IPNV) is an important cause of mortality and economic loss across all species of commercially farmed salmonids, and genetic variation in survival to IPN challenge has been previously demonstrated. In order to exploit this variation in the development of resistant strains, robust procedures are required to quantify the extent of genetic variation and to provide estimated breeding values used to select candidates for breeding. This paper applies a recently developed implementation of the Reduced-Animal Mixed-model procedure (RAM) to field data describing percent mortality following IPN epidemics in Scottish farmed Atlantic salmon, covering 1369 full-sib family groups distributed over four years and a total of seven sites. Pedigrees were established through a combination of electronic (PIT) tagging and parentage assignment using microsatellite DNA analysis. Heritabilities between 0.07 and 0.56 (s.e. < 0.04) were obtained, genetic correlations between sites sharing the same families were uniformly high, 0.70 to 0.85, (s.e. < 0.06) and low levels of fullsib family effect due to common environment (proportion of phenotypic variance 0.04, s.e. 0.002) were observed. These results confirmed that exploitable genetic variation exists for mortality to IPNV over a range of epidemiological conditions inherent in field data, which can be used to select strains of salmon with increased resistance to IPNV.

Genetic variations in survival of rohu carp ( Labeo rohita, Hamilton) after Aeromonas hydrophila infection in challenge tests

A challenge test against Aeromonas hydrophila was conducted using 2062 rohu carp ( Labeo rohita) fingerlings obtained from 52 dams and 87 sires (87 full-sib families) of two year-classes (2003 and 2004). Attempts to establish a cohabitant challenge model were not successful. Therefore, fish were challenged by intraperitoneal injection with A. hydrophila in two replicate tanks per year-class, and dead fish were collected hourly. The mortality reached its peak at 16–22 h after challenge and had almost completely stopped after 58 h. The test was terminated after 382 h at which the average survival was 43.9 and 48.9% in the two 2003 year-class tanks, and 77.1 and 35.8% in the two 2004 year-class tanks. Heritability estimates for survival were obtained from sire and dam threshold models (THR) and sire and dam linear repeatability models (LINR). For both types of models the heritability estimates based on data from single tanks were not consistent. For both year-classes, data from one of the two challenged tanks demonstrated significant additive genetic variation in survival during the A. hydrophila infection, whereas the heritability estimates were not significantly different from zero for the other tank. Further, genetic correlation between survivals in the two replicate tanks in each year-class was not significantly different from zero. The differential results from the replicate tanks demonstrate that additional challenge test experiments are needed before firm conclusions can be drawn about the magnitude of additive genetic variation for survival to aeromonasis in rohu carp. A cohabitant challenge model that allows the testing of important defence mechanisms in the skin and mucous membranes of the fish might have been more appropriate. To establish a valid cohabitant challenge model for rohu carp should be given high priority.

Genetic variation in survival, growth, and stem form of Pinus leiophylla in Brazil and South Africa and provenance resistance to pitch canker

Pinus leiophylla is a relatively common pine that occurs in the mountains of western and central Mexico. Between 1987 and 1990, Camcore, North Carolina State University, sampled 11 populations and 309 mother trees of the species to determine patterns of genetic variation in survival, growth and stem form. Fifteen provenance/progeny trials were established in southern Brazil and South Africa across a wide range of sites and assessed at 3, 5 and 8 years of age for height, diameter and stem form. Results indicated that average productivity ranged from 5 to 19m3 ha−1 y−1 depending on the site and that performance was not as competitive as P. patula (South Africa) and P. taeda (Brazil) controls. Provenances from central Mexico (Michoacan) were statistically better in productivity than those from the southern part of the country (Oaxaca), which in turn were superior to those from the northern part of the country (Durango). However, provenances from northern Mexico exhibited superior survival to seed sources fro...

Genetic variation in survival and growth of Eucalyptus globulus ssp. globulus in Ethiopia

Summary A provenance/progeny trial of Eucalyptus globulus ssp. globulus was established at Ilalaa Gojo in the central highlands of Ethiopia in 1990 to identify superior provenances and establish a breeding population for genetic improvement programs. The trial tested a total of 299 open-pollinated families from 52 localities within 17 natural sub-races in Australia, and one local landrace from Ethiopia. Nine years after planting, more than 61% of trees had survived and the overall mean height and diameter at breast height (dbh) of surviving trees were 21.2 m and 16.4 cm respectively. Significant (P < 0.001) differences in survival, height and dbh per tree were found between sub-races; differences among localities within the sub-races were also significant. Eastern and Western Otways, Cape Patton and Strzelecki Ranges in Victoria were the fastest-growing sub-races, and also displayed above—average survival. Sub-races from the Tasmanian mainland performed poorly; the Wilsons Promontory sub-race was the slowest-growing and displayed poor survival. The Ethiopian landrace performed well although it was not adequately represented in the trial. Assuming a coefficient of relationship of 0.4 for open-pollinated families, individual-tree within-sub-race heritabilities for height and dbh were 0.20 ± 0.03 and 0.16 ± 0.02 respectively. We conclude that there is substantial potential for genetic improvement of E. globulus in Ethiopia.

High-Level Resistance to &lt;I&gt;Bacillus thuringiensis&lt;/I&gt; Toxin Cry1Ac and Cadherin Genotype in Pink Bollworm

Resistance to transgenic cotton, Gossypium hirsutum L., producing Bacillus thuringiensis (Bt) toxin Cry1Ac is linked with three recessive alleles of a cadherin gene in laboratory-selected strains of pink bollworm, Pectinophora gossypiella (Saunders), a major cotton pest. Here, we analyzed a strain (MOV97-R) with a high frequency of cadherin resistance alleles, a high frequency of resistance to 10 microg of Cry1Ac per milliliter of diet, and an intermediate frequency of resistance to 1000 microg of Cry1Ac per ml of diet. We selected two strains for increased resistance by exposing larvae from MOV97-R to diet with 1000 microg of Cry1Ac per ml of diet. In both selected strains, two to three rounds of selection increased survival at 1000 microg of CrylAc per ml of diet to at least 76%, indicating genetic variation in survival at this high concentration and yielding >4300-fold resistance relative to a susceptible strain. Variation in cadherin genotype did not explain variation in survival at 1000 microg of Cry1Ac per ml of diet, implying that one or more other loci affected survival at this concentration. This conclusion was confirmed with results showing that when exposure to Cry1Ac stopped, survival at 1000 microg of Cry1Ac per ml of diet dropped substantially, but survival at 10 microg Cry1Ac per ml of diet remained close to 100% and all survivors had two cadherin resistance alleles. Although survival at 1000 microg of Cry1Ac per ml of diet is not required for resistance to Bt cotton, understanding how genes other than cadherin confer increased survival at this high concentration may reveal novel mechanisms of resistance.

Mitochondrial DNA and survival after sepsis: a prospective study

Human genome evolution has been shaped by infectious disease. Although most genetic studies have focused on the immune system, recovery after sepsis is directly related to physiological reserve that is critically dependent on mitochondrial function. We investigated whether haplogroup H, the most common type of mitochondrial DNA (mtDNA) in Europe, contributes to the subtle genetic variation in survival after sepsis. In a prospective study, we included 150 individuals who were sequentially admitted to the intensive care unit in a hospital in Newcastle upon Tyne, UK. After clinical data were obtained, patients underwent mtDNA haplotyping by analysis with PCR and restriction fragment length polymorphism. As endpoints, we used death during the 6-month period or survival at 6 months. Follow-up was complete for all study participants, although the haplotype of two patients could not be reliably determined. On admission to the intensive care unit, the frequency of mtDNA haplogroup H in study patients did not differ between study patients admitted with severe sepsis and 542 age-matched controls from the northeast of England. MtDNA haplogroup H was a strong independent predictor of outcome during severe sepsis, conferring a 2.12-fold (95% CI 1.02-4.43) increased chance of survival at 180 days compared with individuals without the haplogroup H. Although haplogroup H is the most recent addition to the group of European mtDNA, paradoxically it is also the most common. Increased survival after sepsis provides one explanation for this observation. MtDNA haplotyping offers a new means of risk stratification of patients with severe infections, which suggests new avenues for therapeutic intervention.

GENETIC CONSTRAINTS ON MACROEVOLUTION: THE EVOLUTION OF HOST AFFILIATION IN THE LEAF BEETLE GENUS OPHRAELLA.

We hypothesize that the evolution of an ecologically important character, the host associations of specialized phytophagous insects, has been influenced by limitations on genetic variation. Using as a historical framework a phylogenetic reconstruction of the history of host associations in the beetle genus Ophraella (Chrysomelidae), we have employed quantitative-genetic methods to screen four species for genetic variation in larval survival, oviposition (in one species only), and feeding responses to their congeners' host plants, in the Asteraceae. We here report results of studies of one species and evaluate the results from all four. Analysis of half-sib/full-sib families and of progenies of wild females of O. notulata, a specialist on Iva (Ambrosiinae), provided evidence of genetic variation in larval consumption of five of six test plants and in adult consumption of four of six. Larval mortality was complete on five plants; only on Ambrosia, a close relative of the natural host, was there appreciable, and genetically variable, survival. Oviposition on Ambrosia showed marginally significant evidence of genetic variation; a more distantly related plant elicited no oviposition at all. In compiling results from four Ophraella species, reported in this and two other papers, we found no evidence of genetic variation in 18 of 39 tests of feeding responses and 14 of 16 tests of larval survival on congeners' hosts. This result is consistent with the hypothesis that absence or paucity of genetic variation may constrain or at least bias the evolution of host associations. The lower incidence of genetic variation in survival than in feeding behavior may imply, according to recent models, that avoidance is a more common evolutionary response to novel plants than adaptation. The usually great disparity between mean performance on congeners' hosts and the species' natural hosts, and an almost complete lack of evidence for negative genetic correlations, argue against the likelihood that speciation has occurred by sympatric host shift. The presence versus apparent absence of genetic variation in consumption was correlated with the propinquity of relationship between the beetle species tested and the species that normally feeds on the test plant, suggesting that the history of host shifts in Ophraella has been guided in part by restrictions on genetic variation. It was also correlated with the propinquity of relationship between a test plant and the beetle's natural host. The contributions of plant relationships and insect relationships, themselves correlated in part, to the pattern of genetic variation, are not readily distinguishable, but together accord with phylogenetic evidence that these and other phytophagous insects adapt most readily to related plants. In this instance, therefore, the macroevolution of an ecologically important character appears to have been influenced by genetic constraints. We hypothesize that absence of the structural prerequisites for genetic variation in complex characters may affect genetic variation and the trajectory of evolution.

Direct and indirect effects of plant genetic variation on enemy impact

Abstract. The Tritrophic and Enemy Impact concepts predict that natural enemy impact varies: (a) among plant genotypes and (b) may depend on the abundance of heterospecific herbivores, respectively. I tested these predictions using three herbivore species on potted, cloned genotypes of Salik sericea Marshall in a common garden experiment. Densities of the leaf miner (Phyllonorycter salicifoliella (Chambers)) and two leaf galling sawflies (Phyllocolpa nigrita (Marlatt) and Phyllocolpa eleanorae Smith and Fritz) varied significantly among willow clones, indicating genetic variation in resistance. Survival and natural enemy impact caused by egg and larval parasitoids and/or unknown predators differed significantly among willow clones for each of the three herbivore species, indicating genetic variation in survival and enemy impact. Survival of Phyllonorycter was negatively density‐dependent among clones. Survival of Phyllonorycter and Phyllocolpa eleanorae were positively correlated with densities of heterospecific herbivores among clones and parasitism of these species were negatively correlated with densities of the same heterospecific herbivores among clones. At least for Phyllonorycter this positive correlation may suggest either facilitation of survival between herbivore species, which do not share natural enemies, or an apparent interaction caused by host plant genetic variation. Among clones, egg parasitism of Phyllocolpa eleanorae was weakly positively correlated with density of Phyllocolpa nigrita. Since these species share the same Trichogramma egg parasitoid, this interaction could support the hypothesis of apparent competition.

Effects of exposure to short‐term heat stress on fitness components in Drosophila melanogaster

AbstractEffects of thermal stress on survival and reproductive success in ten recently collected isofemale lines of Drosophila melanogaster were compared for flies treated as follows: always held at 25° C, placed in an incubator set at 37° C for 120 min, or exposed to 40° C in an incubator for 90 min, with or without previous exposure to 37° C. Short‐term exposure to the higher temperature greatly reduced adult survival, the mating frequency of males and females, and female fecundity, which was measured as offspring produced over ten days. Male fertility, measured as the progeny produced by a female mated once, differed little among treatments. Previous exposure to a high, but non‐lethal, temperature before exposure to the higher one, improved survival of males and females, and improved offspring production of females. Genetic variation was present among lines for offspring production, but genetic variation for survival was not significant, and genotype by environment interactions for fitness components of females were small. These results indicated low genetic variation in thermal resistance in the studied population, such that a threshold for temperature stress probably exists, above which local extinction is more likely than the evolution of resistance.

Genetic parameters for calving ease and survival at birth in Angus field data1

Calving performance records from the American Angus Herd Improvement Registry files were used to estimate variance components for calving ease and survival to 24 h. Genetic parameters for direct and maternal effects were estimated by using a sire-maternal grandsire model. Data included two independent samples of 19 and 34 herds with complete calving information. Maternal variance for calving ease was much larger than the variance for the direct effect of the sire. Maternal heritability for calving ease was .27 and .20 in the two samples of herds, respectively. Heritabilities for direct effects were .21 and .07. The genetic correlations between direct and maternal effects were -.93 and -.80. There was little genetic variation in survival at birth. Parameter estimates were within the allowable parameter space in the sample of 19 herds. Heritability for the direct effect of the sire on survival was .04. Maternal heritability was .09, and the direct-maternal correlation was -.85.